Optical system, image projection apparatus, and imaging apparatus

Abstract

The present disclosure is directed to an optical system internally having an intermediate imaging position that is conjugated to a magnification conjugate point on a magnification side and a reduction conjugate point on a reduction side, respectively, the optical system including: a magnification optical system having A (A is an integer of three or more) pieces of lens elements, positioned on the magnification side with respect to the intermediate imaging position; and a relay optical system having B (B is an integer of two or more) pieces of lens elements, positioned on the reduction side with respect to the intermediate imaging position. A first lens group composed of β pieces (β is one or more and less than B) of lens elements positioned first from the magnification side in the relay optical system has a negative power.

The invention claimed is: 
     
       1. An optical system internally having an intermediate imaging position MI that is conjugated to a magnification conjugate point on a magnification side and a reduction conjugate point on a reduction side, respectively, the optical system including:
 a magnification optical system having A (A is an integer of three or more) pieces of lens elements, positioned on the magnification side with respect to the intermediate imaging position; and 
 a relay optical system having B (B is an integer of two or more) pieces of lens elements, positioned on the reduction side with respect to the intermediate imaging position MI, 
 wherein a first lens group composed of β pieces (β is one or more and less than B) of lens elements positioned first from the magnification side in the relay optical system has a negative power, 
 wherein a lens positioned first from the reduction side in the relay optical system is fixed during focusing, and at least a first lens element in the magnification optical system moves along the optical axis during the focusing, 
 wherein the magnification optical system has a second focus lens group composed of one or two pieces of lens elements including the first lens element positioned first from the magnification side, and 
 wherein the second focus lens group corrects field curvature aberration by moving along the optical axis after focusing. 
 
     
     
       2. The optical system according to  claim 1 , wherein the magnification optical system satisfies the following condition (3):
   18<| fFG 2/ fw|< 120  (3)
 
 where, fFG 2  is a focal length of the second focus lens group, and fw is a focal length of the entire optical system at the wide-angle end. 
 
     
     
       3. An optical system internally having an intermediate imaging position MI that is conjugated to a magnification conjugate point on a magnification side and a reduction conjugate point on a reduction side, respectively, the optical system including:
 a magnification optical system having A (A is an integer of three or more) pieces of lens elements, positioned on the magnification side with respect to the intermediate imaging position; and 
 a relay optical system having B (β is an integer of two or more) pieces of lens elements, positioned on the reduction side with respect to the intermediate imaging position MI, 
 wherein a first lens group composed of β pieces (β is one or more and less than B) of lens elements positioned first from the magnification side in the relay optical system has a negative power, 
 wherein the first lens group is fixed during zooming, and 
 wherein the magnification optical system has a second focus lens group that corrects field curvature aberration by moving along the optical axis after focusing. 
 
     
     
       4. The optical system according to  claim 3 , wherein the magnification optical system is fixed during zooming, and a part or all of the lens elements of the relay optical system excluding the first lens group move along the optical axis during zooming. 
     
     
       5. The optical system according to  claim 1 , satisfying the following condition (1):
   1< fs 1/ fw< 100  (1)
 
 where, fs 1  is a focal length of the first lens group, and fw is a focal length of the entire optical system at the wide-angle end. 
 
     
     
       6. The optical system according to  claim 5 , wherein the magnification optical system Op has a first focus lens group composed of α pieces (α is three or more and less than A) of lens elements including the first lens element, and
 satisfy the following condition (2):
   2<| fFG 1/ fw|< 10  (2)
 
 
 where, fFG 1  is a focal length of the first focus lens group, and fw is a focal length of the entire optical system at the wide-angle end. 
 
     
     
       7. An optical system internally having an intermediate imaging position MI that is conjugated to a magnification conjugate point on a magnification side and a reduction conjugate point on a reduction side, respectively, the optical system including:
 a magnification optical system having A (A is an integer of three or more) pieces of lens elements, positioned on the magnification side with respect to the intermediate imaging position; and 
 a relay optical system having B (B is an integer of two or more) pieces of lens elements, positioned on the reduction side with respect to the intermediate imaging position MI, 
 wherein a first lens group composed of β pieces (β is one or more and less than B) of lens elements positioned first from the magnification side in the relay optical system has a negative power, 
 wherein the relay optical system is fixed during focusing, and a part or all of the lens elements in the magnification optical system move along the optical axis during focusing, and 
 wherein the magnification optical system has a second focus lens group that corrects field curvature aberration by moving along the optical axis after focusing. 
 
     
     
       8. The optical system according to  claim 7 , satisfying the following condition (4):
   1.0<| ff/fw|< 5  (4)
 
 where, ff is a focal length of the magnification optical system, and fw is a focal length of the entire optical system at the wide-angle end. 
 
     
     
       9. The optical system according to  claim 7 , satisfying the following condition (5):
   1.5<| fr/fw|< 5  (5)
 
 where, fr is a focal length of the relay optical system at the wide-angle end, and fw is a focal length of the entire optical system at the wide-angle end. 
 
     
     
       10. The optical system according to  claim 1 , wherein the relay optical system is constituted of any one of: (a) a first lens group having a negative power, a second lens group having a positive power, a third lens group having a positive or negative power, a fourth lens group having a positive power, arranged in order from the magnification side to the reduction side; and (b) a first lens group having a negative power, a second lens group having a positive power, a third lens group having a negative power, a fourth lens group having a positive power, and a fifth lens group having a positive power, arranged in order from the magnification side to the reduction side. 
     
     
       11. The optical system according to  claim 1 , satisfying the following condition (6):
   |ω|>60  (6)
 
 where, ω is a maximum half angle of view at the wide-angle end. 
 
     
     
       12. An image projection apparatus comprising:
 the optical system according to  claim 1 ; and 
 an image forming element that generates an image to be projected through the optical system onto a screen. 
 
     
     
       13. An imaging apparatus comprising:
 the optical system according to  claim 1 ; and 
 an imaging element that receives an optical image formed by the optical system to convert the optical image into an electrical image signal.